Ligand fragmentations

The 31P and H study revealed the configuration of the central atom and the conformation of the cyclic ligand fragments, as well as the orientation of M—P bonds. The Pt—P bond is equatorial in the 1,3,5-diazaphosphorinane cycle. 

It is becoming increasingly apparent that a very extensive chemistry is associated with the dimetal species (1), and (3) - (13). Three types of reaction may be identified (i) aSTdition of other metal ligand fragments, discussed in the next Section, (ii) replacement of peripheral ligands on the metal centres, and (iii) reactions at the bridging carbon atom. One example of (ii) and (iii) will suffice to illustrate the scope and potential for new chemistry. 

Clusters of Class B may be prepared by adding appropriate metal ligand fragments to the dimetal species. Thus treatment of (3) with [Fe2(C0)9l affords (34), and similarly (4) reacts with [Fe2(C0),J to give (35)(9). 

Although the chemistry of bi- and poly-nuclear vinylidene complexes is beyond the scope of this chapter, several examples of the interaction of metal-vinylidene fragments with a second metal-ligand fragment have been described. This type of reaction usually produces complexes containing bridging vinylidene ligands (Equation 1.21) ... 

Cumulenylidene complexes constitute a class of organometallic compounds in which a chain of sp-hybridized carbon atoms is terminated by a sp -hybridized carbon atom (CR2 group) at one end and by a metal-ligand fragment (Lr,M) at the other end. 

The metal-ligand fragment L M, the number of carbon atoms x, and the substituents at the terminal sp -carbon may vary considerably and, correspondingly, the properties and reactivities. The early members of the series of cumulenylidene complexes (x=l, 2, 3 carbene, vinylidene and allenylidene complexes) have established themselves as invaluable building blocks in stoichiometric synthesis and as highly potent catalyst precursors. The higher members might potentially be very useful candidates for application as one-dimensional wires and in opto-electronic devices. 

Independent of the chain length, the substituents R and the metal-ligand fragment L M the LUMO in d and d complexes is predominantly localized on the odd carbon atoms. Therefore, nucleophiles are expected to add to the odd carbon atoms in the chain.The HOMO in d and d complexes has contributions mainly from the metal and the carbon atoms in even positions of the chain. As a consequence, electrophiles are expected to add either to the metal or to even-numbered carbon atoms. Deviating from these more general results, the HOMO in [(CO)5Cr=(C)4H2] has been calculated to be more evenly distributed along the chain with major components from the odd-numbered carbon atoms Cl and C3 [10-13]. 

DFT calculations indicate that the LUMO in d and d complexes is predominantly localized on the odd carbon atoms independent of the chain length, the substituents R and the metal-ligand fragment L M. Therefore, nucleophiles are expected to add to the odd carbon atoms of the chain in butatrienylidene as well as in pentatetraeny-lidene complexes. 

The LUMO in d pentatetraenylidene complexes is predominantly localized on the odd carbon atoms and to a lesser extent on the metal. The coefficients on Cl and C3 are very similar, independent of the metal-ligand fragment and the terminal substituent. The coefficient at C5 is somewhat larger. In square-planar d rhodium and iridium complexes the coefficient at the metal is comparable to that on C5 and is larger than those on Cl and C3. Thus, a nucleophilic attack at the metal of d complexes has also to be taken into account. 

Simionescu and coworkers (36) also carried out for the first time mechanical reactions leading to complex metal chelates with macromolecular ligands. Fragments formed from the mechanical condensation of polyethylene tereph-thalate with ethylene diamine serve as ligands for ferric chloride. The reaction was performed in a vibromill (amplitude 4 mm, 1475 rpm at 18° C). 

The interaction of formaldehyde and thioformaldehyde with some group 8 metal-ligand fragments [Ru(CO)4,40 Fe(CO)2(PH3)241] in the rf conformation has been analyzed by the Hartree-Fock-Slater transition-state method... 

Mononuclear heterocarbonyl complexes usually adopt either a tj1 or a rf configuration. Complexes of d6 metal-ligand fragments such as M(CO)5 or MLiL2(775-C5H5) may be regarded as borderline cases between rf and rf preferences. The coexistence of the two forms was reported for the first time in 1984.44 An equilibrium between rf and rf isomers of [M(CO)5 Se=... 

Scheme 2. M Li, represents a metal ligand fragment having a vacant coordination site this is a species generally formed by loss of a labile ligand (e.g., CO, C2H4, THF) from a complex.

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